Common packet channel

ABSTRACT

An improvement to a code-division-multiple-access (CDMA) system employing spread-spectrum modulation, with the CDMA system having a base station (BS) and a plurality of remote stations. The base station has a BS-spread-spectrum transmitter and a BS-spread-spectrum receiver. A remote station has an RS-spread-spectrum transmitter and an RS-spread-spectrum receiver. The BS transmitter transmits a broadcast common-synchronization channel, which includes a frame-timing signal. The broadcast common-synchronization channel has a common chip-sequence signal, which is common to the plurality of remote stations. In response to the RS-spread-spectrum receiver receiving the broadcast common-synchronization channel, and determining frame timing from the frame-timing signal, an RS-spread-spectrum transmitter transmits an access-burst signal. The BS-spread-spectrum transmitter, responsive to the BS-spread-spectrum receiver receiving the access-burst signal, transmits an acknowledgment signal. In response to the first RS-spread-spectrum receiver receiving the acknowledgment signal, the first RS-spread-spectrum transmitter transmits a spread-spectrum signal having data.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of application Ser. No. 09/941,756filed Aug. 30, 2001, now U.S. Pat. No. 6,717,975, which is aContinuation of application Ser. No. 09/679,367 filed Oct. 5, 2000, nowU.S. Pat. No. 6,301,286, which is a Continuation of application Ser. No.09/273,508 filed Mar. 22, 1999, now U.S. Pat. No. 6,169,759.

BACKGROUND OF THE INVENTION

This invention relates to spread-spectrum communications, and moreparticularly to code-division-multiple-access (CDMA) cellular,packet-switched systems.

DESCRIPTION OF THE RELEVANT ART

Presently proposed for a standard is a random-access burst structurewhich has a preamble followed by a data portion. The preamble has 16symbols, the preamble sequence, spread by an orthogonal Gold code. Amobile station acquires chip and frame synchronization.

SUMMARY OF THE INVENTION

A general object of the invention is an efficient method for packet datatransfer on CDMA systems.

Another object of the invention is high data throughput and low delay.

According to the present invention, as embodied and broadly describedherein, an improvement to a code-division-multiple-access (CDMA) systememploying spread-spectrum modulation, is provided. The CDMA system has abase station (BS) and a plurality of remote stations. The base stationhas BS-spread-spectrum transmitter and a BS-spread-spectrum receiver.Each of the plurality of remote stations has an RS-spread-spectrumtransmitter and an RS-spread-spectrum receiver. The method comprises thesteps of transmitting from BS-spread-spectrum transmitter, a broadcastcommon-synchronization channel. The broadcast common-synchronizationchannel has a common chip-sequence signal common to the plurality ofremote stations. Further, the broadcast common-synchronization channelhas a frame-timing signal.

A first RS-spread-spectrum receiver, located at a first remote station,the method includes the step of receiving the broadcastcommon-synchronization channel. From the received broadcastcommon-synchronization channel, the steps include determining frametiming at the first RS-spread-spectrum receiver from the frame-timingsignal.

At a first RS-spread-spectrum transmitter, located at the first remotestation, the steps include transmitting an access-burst signal. Theaccess-burst signal has a plurality of segments. A segment is aninterval in time of the access-burst signal. Each segment has a preamblefollowed by a pilot signal. The plurality of segments preferably alsohas a plurality of power levels, respectively. Preferably, the pluralityof power levels increase sequentially, with each segment.

At the BS spread-spectrum receiver the steps include receiving theaccess-burst signal at a detected-power level. In response to receivingthe access-burst signal, from the BS-spread-spectrum transmitter, thesteps include transmitting to the first RS-spread-spectrum receiver anacknowledgment signal.

At the first RS-spread-spectrum receiver the steps include receiving theacknowledgment signal. In response to receiving the acknowledgmentsignal, the steps include transmitting from the first RS-spread-spectrumtransmitter, to said BS-spread-spectrum receiver, a spread-spectrumsignal having data.

Additional objects and advantages of the invention are set forth in partin the description which follows, and in part are obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention also may be realized and attained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 is a common packet channel system block diagram with a commoncontrol downlink channel;

FIG. 2 is common packet channel system block diagram with a dedicateddownlink channel;

FIG. 3 is a block diagram of a base station receiver and transmitter forcommon packet channel;

FIG. 4 is a block diagram of a remote station receiver and transmitterfor common packet channel;

FIG. 5 is a timing diagram for access burst transmission;

FIG. 6 illustrates common packet channel access burst of FIG. 5 using acommon control downlink channel;

FIG. 7 illustrates common packet channel access of FIG. 5 using adedicated downlink channel;

FIG. 8 shows the structure of the preamble;

FIG. 9 illustrates preamble and pilot formats;

FIG. 10 is a common packet channel timing diagram and frame format ofthe down link common control link; and

FIG. 11 illustrates frame format of common packet channel, packet data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference now is made in detail to the present preferred embodiments ofthe invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals indicate like elementsthroughout the several views.

The common-packet channel is a new and novel uplink transport channelfor transmitting variable size packets from a mobile station to a basestation within listening range, without the need to obtain a two waylink with any one or set of base stations. The channel resourceallocation is contention based; that is, a number of mobile stationscould at any time contend for the same resources, as found in an ALOHAsystem.

In the exemplary arrangement shown in FIG. 1, common-packet channelprovides an improvement to a code-division-multiple-access (CDMA) systememploying spread-spectrum modulation. The CDMA system has a plurality ofbase stations (BS) 31, 32, 33 and a plurality of remote stations (RS).Each remote station 35 has an RS-spread-spectrum transmitter and anRS-spread-spectrum receiver. An uplink is from the remote station 35 toa base station 31. The uplink has the common-packet channel (CPCH). Adownlink is from a base station 31 to the remote station 35, and isdenoted a common-control channel (CCCH). The common-control channel hascommon signaling used by the plurality of remote stations.

An alternative to the common-control channel, but still using thecommon-packet channel, is the downlink dedicated physical channel(DPCH), shown in FIG. 2. The dedicated downlink channel, has signalingthat is used for controlling a single remote station.

As illustratively shown in FIG. 3, a BS spread-spectrum transmitter anda BS spread-spectrum receiver is shown. The BS spread-spectrumtransmitter and the BS spread-spectrum receiver are located at the basestation 31. The BS spread-spectrum receiver includes an antenna 309coupled to a circulator 310, a receiver radio frequency (RF) section311, a local oscillator 313, a quadrature demodulator 312, and ananalog-to-digital converter 314. The receiver RF section 311 is coupledbetween the circulator 310 and the quadrature demodulator 312. Thequadrature demodulator is coupled to the local oscillator 313 and to theanalog to digital converter 314. The output of the analog-to-digitalconverter 315 is coupled to a programmable-matched filter 315.

A preamble processor 316, pilot processor 317 and data-and-controlprocessor 318 are coupled to the programmable-matched filter 315. Acontroller 319 is coupled to the preamble processor 316, pilot processor317 and data-and-control processor 318. A de-interleaver 320 is coupledbetween the controller 319 and a forward-error-correction (FEC) decoder321.

The BS spread-spectrum transmitter includes a forward-error-correction(FEC) encoder 322 coupled to an interleaver 323. A packet formatter 324is coupled to the interleaver 323 and to the controller 319. A variablegain device 325 is coupled between the packet formatter 324 and aproduct device 326. A spreading-sequence generator 327 is coupled to theproduct device 326. A digital-to-analog converter 328 is coupled betweenthe product device 328 and quadrature modulator 329. The quadraturemodulator 329 is coupled to the local oscillator 313 and a transmitterRF section 330. The transmitter RF section 330 is coupled to thecirculator 310.

The controller 319 has control links coupled to the analog-to-digitalconverter 314, programmable-matched filter 315, preamble processor 316,the digital-to-analog converter 328, the spreading sequence generator327, the variable gain device 325, the packet formatter 324, thede-interleaver 320, the FEC decoder 321, the interleaver 323 and the FECencoder 322.

A received spread-spectrum signal from antenna 309 passes throughcirculator 310 and is amplified and filtered by receiver RF section 311.The local oscillator 313 generates a local signal which quadraturedemodulator 312 uses to demodulator in-phase and quadrature phasecomponents of the received spread-spectrum signal. The analog-to-digitalconverter 314 converts the in-phase component and the quadrature-phasecomponent to a digital signal. These functions are well known in theart, and variations to this block diagram can accomplish the samefunction.

The programmable-matched filter 315 despreads the receivedspread-spectrum signal. A correlator, as an alternative, may be used asan equivalent means for despreading the received spread-spectrum signal.

The preamble processor 316 detects the preamble portion of the receivedspread-spectrum signal. The pilot processor detects and synchronizes tothe pilot portion of the received spread-spectrum signal. The data andcontrol processor detects and processes the data portion of the receivedspread-spectrum signal. Detected data passes through the controller 319to the de-interleaver 320 and FEC decoder 321. Data and signaling areoutputted from the FEC decoder 321.

In the BS transmitter, data are FEC encoded by FEC encoder 322, andinterleaved by interleaver 323. The packet formatter formats data,signaling, acknowledgment signal, collision detection signal, pilotsignal and transmitting power control (TPC) signal into a packet. Thepacket is outputted from packet formatter, and the packet level isamplified or attenuated by variable gain device 325. The packet isspread-spectrum processed by product device 326, with a spreadingchip-sequence from spreading-sequence generator 327. The packet isconverted to an analog signal by digital-to-analog converter 328, andin-phase and quadrature-phase components are generated by quadraturemodulator 329 using a signal from local oscillator 313. The packet istranslated to a carrier frequency, filtered and amplified by transmitterRF section 330, and then passes through circulator 310 and is radiatedby antenna 309.

In the illustrative embodiment shown in FIG. 4, a RS spread-spectrumtransmitter and a RS spread-spectrum receiver are shown. The RSspread-spectrum transmitter and the MSRS spread-spectrum receiver arelocated at the remote station 35, shown in FIG. 1. The RSspread-spectrum receiver includes an antenna 409 coupled to a circulator410, a receiver radio frequency (RF) section 411, a local oscillator413, a quadrature demodulator 412, and an analog-to-digital converter414. The receiver RF section 411 is coupled between the circulator 410and the quadrature demodulator 412. The quadrature demodulator iscoupled to the local oscillator 413 and to the analog to digitalconverter 414. The output of the analog-to-digital converter 415 iscoupled to a programmable-matched filter 415.

An acknowledgment detector 416, pilot processor 417 and data-and-controlprocessor 418 are coupled to the programmable-matched filter 415. Acontroller 419 is coupled to the acknowledgment detector 416, pilotprocessor 417 and data-and-control processor 418. A de-interleaver 420is coupled between the controller 419 and a forward-error-correction(FEC) decoder 421.

The RS spread-spectrum transmitter includes a forward-error-correction(FEC) encoder 422 coupled to an interleaver 423. A packet formatter 424is coupled through a multiplexer 451 to the interleaver 423 and to thecontroller 419. A preamble generator 452 and a pilot generator 453 forthe preamble are coupled to the multiplexer 451. A variable gain device425 is coupled between the packet formatter 424 and a product device426. A spreading-sequence generator 427 is coupled to the product device426. A digital-to-analog converter 428 is coupled between the productdevice 428 and quadrature modulator 429. The quadrature modulator 429 iscoupled to the local oscillator 413 and a transmitter RF section 430.The transmitter RF section 430 is coupled to the circulator 410.

The controller 419 has control links coupled to the analog-to-digitalconverter 414, programmable-matched filter 415, acknowledgment detector416, the digital-to-analog converter 428, the spreading sequencegenerator 427, the variable gain device 425, the packet formatter 424,the de-interleaver 420, the FEC decoder 421, the interleaver 423, theFEC encoder 422, the preamble generator 452 and the pilot generator 453.

A received spread-spectrum signal from antenna 409 passes throughcirculator 410 and is amplified and filtered by receiver RF section 411.The local oscillator 413 generates a local signal which quadraturedemodulator 412 uses to demodulate in-phase and quadrature phasecomponents of the received spread-spectrum signal. The analog-to-digitalconverter 414 converts the in-phase component and the quadrature-phasecomponent to a digital signal. These functions are well known in theart, and variations to this block diagram can accomplish the samefunction.

The programmable-matched filter 415 despreads the receivedspread-spectrum signal. A correlator, as an alternative, may be used asan equivalent means for despeading the received spread-spectrum signal.

The acknowledgment detector 416 detects the a acknowledgment in thereceived spread-spectrum signal. The pilot processor detects andsynchronizes to the pilot portion of the received spread-spectrumsignal. The data and control processor detects and processes the dataportion of the received spread-spectrum signal. Detected data passesthrough the controller 419 to the de-interleaver 420 and FEC decoder421. Data and signaling are outputted from the FEC decoder 421.

In the RS transmitter, data are FEC encoded by FEC encoder 422, andinterleaved by interleaver 423. The preamble generator 452 generates apreamble and the pilot generator 453 generates a pilot for the preamble.The multiplexer 451 multiplexes the data, preamble and pilot, and thepacket formatter 424 formats the preamble, pilot and data into acommon-packet channel packet. Further, the packet formatter formatsdata, signaling, acknowledgment signal, collision detection signal,pilot signal and TPC signal into a packet. The packet is outputted frompacket formatter, and the packet level is amplified or attenuated byvariable gain device 425. The packet is spread-spectrum processed byproduct device 426, with s spreading chip-sequence fromspreading-sequence generator 427. The packet is converted to an analogsignal by digital-to-analog converter 428, and in-phase andquadrature-phase components are generated by quadrature modulator 429using a signal from local oscillator 413.

Referring to FIG. 5, the base station transmits a common-synchronizationchannel, which has a frame time duration T_(F). Thecommon-synchronization channel has a common chip-sequence signal, whichis common to the plurality of remote stations communicating with theparticular base station. In a particular embodiment, the time T_(F) ofone frame is ten milliseconds. Within one frame, there are eight accessslots. Each access slot lasts 1.25 milliseconds. Timing for the accessslots is the frame timing, and the portion of the common-synchronizationchannel with the frame timing is denoted the frame-timing signal. Theframe-timing signal is the timing a remote station uses in selecting anaccess slot in which to transmit an access-burst signal.

A first remote station attempting to access the base station, has afirst RS-spread-spectrum receiver for receiving the commonsynchronization channel, broadcast from the base station. The firstRS-spread-spectrum receiver determines frame timing from theframe-timing signal.

A first RS-spread-spectrum transmitter, located at the first remotestation, transmits an access-burst signal. An access burst signal, asshown in FIG. 5, starts at the beginning of an access slot, as definedby the frame timing portion of the common-synchronization channel.

FIG. 6 illustratively shows the common-packet channel access burstformat, for each access-burst signal. Each access-burst signal has aplurality of segments. Each segment has a preamble followed by a pilotsignal. The plurality of segments has a plurality of power levels,respectively. More particularly, the power level of each segmentincreases with each subsequent segment. Thus, a first segment has afirst preamble and pilot, at a first power level P₀. A second segmenthas a second preamble and a second pilot, at a second power level P₁.The third segment has a third preamble and a third pilot at a thirdpower level P₂. The first preamble, the second preamble, the thirdpreamble, and subsequent preambles, may be identical or different. Thepower level of the pilot preferably is less than the power level of thepreamble. A preamble is for synchronization, and a corresponding pilot,which follows a preamble, is to keep the BS spread-spectrum receiverreceiving the spread-spectrum signal from the remote station, once apreamble is detected.

A subsequent increase or decrease of power levels is basically a closedloop power control system. Once a BS spread-spectrum receiver detects apreamble from the remote station, the BS spread-spectrum transmittersends an acknowledgment (ACK) signal.

Referring to FIG. 4, the preamble is generated by preamble generator 452and the pilot is generated by pilot generator 453. A preamble format isshown in FIG. 8. The preamble format with a pilot is shown in FIG. 9.The multiplexer 451, with timing from the controller 419, selects thepreamble then a corresponding pilot, for packet formatter 424. A seriesof preambles and pilots may be generated and made as part of the packetby packet formatter 424. The preambles and pilots can have their powerlevel adjusted either in the preamble generator 452 and pilot generator453, or by the variable gain device 425.

The BS spread-spectrum receiver receives the access-burst signal at adetected-power level. More particularly, the access-burst signal has theplurality of preambles at a plurality of power levels, respectively.When a preamble with sufficient power level is detected at the BSspread-spectrum receiver, then an acknowledgment (ACK) signal istransmitted from the BS spread-spectrum transmitter. The ACK signal isshown in FIG. 6, in response to the fourth preamble having sufficientpower for detection by the BS spread-spectrum receiver.

FIG. 3 shows the preamble processor 316 for detecting the preamble andthe pilot processor 317 for continuing to receive the packet afterdetecting the preamble. Upon detecting the preamble, the processor 319initiates an ACK signal which passes to packet formatter 324 and isradiated by the BS spread-spectrum transmitter.

The first RS-spread-spectrum receiver receives the acknowledgmentsignal. Upon receiving the ACK signal, the first RS-spread-spectrumtransmitter transmits to the BS-spread-spectrum receiver, aspread-spectrum signal having data. The data is shown in FIG. 6, intime, after the ACK signal. The data includes a collision detection (CD)portion of the signal, referred to herein as a collision detectionsignal, and message.

In response to each packet transmitted from the RS spread-spectrumtransmitter, the BS receiver detects the collision detection portion ofthe data, and retransmits the data field of the collision detectionportion of the data to the remote station. FIG. 10 shows the timingdiagram for re-transmitting the collision detection field. There areseveral slots for collision detection retransmission, which can be usedfor re-transmitting the collision detection field for several remotestations. If the collision detection field were correctly re-transmittedto the remote station, then the remote station knows its packet issuccessfully received by the base station. If the collision detectionfield were not correctly re-transmitted by the base station, then theremote station assumes there is a collision with a packet transmitted byanother remote station, and stops further transmission of the data.

FIG. 11 shows a frame format of a common-packet channel data payload.

In operation, an overview of the way this transport mechanism is used isas follows. A remote station (RS) upon power up searches fortransmission from nearby base stations. Upon successful synchronizationwith one or more base stations, the Remote station receives thenecessary system parameters from a continuously transmitted by all basestations broadcast control channel (BCCH). Using the informationtransmitted from the BCCH, the remote station can determine variousparameters required when first transmitting to a base station.Parameters of interest are the loading of all the base station in thevicinity of the remote station, their antenna characteristics, spreadingcodes used to spread the downlink transmitted information, timinginformation and other control information. With this information, theremote station can transmit specific waveforms in order to capture theattention of a nearby base station. In the common packet channel theremote station, having all the necessary information from the nearbybase station, it starts transmitting a particular preamble from a set ofpredefined preambles, at a well selected time intervals. The particularstructure of the preamble waveforms is selected on the basis thatdetection of the preamble waveform at the base station is to be as easyas possible with minimal loss in detectability.

The physical common packet channel (CPCH) is used to carry the CPCH. Itis based on the well known Slotted ALOHA approach. There is a number ofwell defined time offsets relative to the frame boundary of a downlinkreceived BCCH channel. These time offsets define access slots. Thenumber of access slots is chosen according to the particular applicationat hand. As an example, shown in FIG. 5, eight access slots are spaced1.25 msec apart in a frame of 10-msec duration.

According to FIG. 5, a remote station picks an access slot in a randomfashion and tries to obtain a connection with a base station bytransmitting a preamble waveform. The base station is able to recognizethis preamble, and is expecting its reception at the beginning of eachaccess slot. The length of the access burst is variable and the lengthof the access burst is allowed to vary from a few access slots to manyframe durations. The amount of data transmitted by the remote stationcould depend on various factors. Some of those are: class capability ofthe remote station, prioritization, the control information transmitteddown by the base station, and various bandwidth management protocolsresiding and executed at the base station. A field at the beginning ofthe data portion signifies the length of the data.

The structure of the access burst is shown in FIG. 6. The access burststarts with a set of preambles of duration T_(P) whose power isincreased in time from preamble to preamble in a step-wise manner. Thetransmitted power during each preamble is constant. For the durationT_(D) between preambles the access burst consists of a pilot signaltransmitted at a fixed power level ratio relative to the previouslytransmitted preamble. There is a one to one correspondence between thecode structure of the preamble and the pilot signal. The pilot signalcould be eliminated by setting it to a zero power level.

The transmission of the preambles ceases because either the preamble hasbeen picked up, detected, by the base station, and the base station hasresponded to the remote station with a layer one acknowledgment L1 ACKwhich the remote station has also successfully received. Transmission ofthe preamble ceases also if the remote station has transmitted themaximum allowed number of preambles M_(P). Upon receiving this L1 ACKthe remote station starts transmission of its data. Once the remotestation has transmitted more than M_(P) preambles, it undergoes a forcedrandom back off procedure. This procedure forces the remote station todelay its access burst transmission for a later time. The random backoff procedure could be parameterized based on the priority statues ofthe Remote station. The amount by which the power is increased frompreamble to preamble is D_(P) which is either fixed for all cells at alltimes or it is repeatedly broadcast via the BCCH. Remote stations withdifferent priority status could use a power increase which depends on apriority status assigned to the remote station. The priority statuscould be either predetermined or assigned to the remote station afternegotiation with the base station.

The Preamble Signal Structure

There is a large set of possible preamble waveforms. Every base stationis assigned a subset of preambles from the set of all preamble waveformsin the system. The set of preambles a base station is using is broadcastthrough its BCCH channel. There are many ways of generating preamblewaveforms. One existing way is to use a single orthogonal Gold code perpreamble from the set of all possible orthogonal Gold codes of length L.A preamble could then be constructed by repeating the Gold code a numberof times N to transmit a length N complex sequence. For example if Adenotes the orthogonal Gold code and G_(i)={g_(i,0) g_(i,1) g_(i,2) . .. g_(i,N−1)}, a length N complex sequence, then a preamble could beformed as shown in FIG. 8, where, g_(i,j), j=0, . . . ,N−1, multipliesevery element in A. Normally the sets of G_(i)'s are chosen to beorthogonal to each other. This will allow for a maximum of N possiblewaveforms. The total number of possible preambles is then L*N.

The preferred approach is to use different codes rather than a singlerepeating code in generating each preamble. In that case, if L possiblecodes, not necessarily Gold Codes, were possible, designated by A₀, A₁,. . . A_(L−1), then possible preambles will be as shown in FIG. 8. Theorder of the A_(i)'s can be chosen so that identical codes are not usedin the same locations for two different preambles. A similar approachcould be used to form the pilot signals.

The Downlink Common Control Channel

In FIG. 10, the downlink common control channel structure for even andodd slots is shown. The even slots contain reference data and controldata. The pilot symbols are used to derive a reference for demodulatingthe remaining control symbols. The control symbols are made of transportframe indicator (TFI) symbols, power control (PC) symbols, collisiondetection (CD) symbol and signaling symbols (SIG). The odd slots containall the information that the even slots contain plus an acknowledgment(ACK) signal. Odd slots do not include collision detection fields.

The uplink CPCH is shown over the last transmitted preamble. After thelast transmitted preamble, the base station has successfully detectedthe transmission of the last transmitted preamble and transmits back theacknowledgment signal. During the same time, the remote station is tunedto receive the ACK signal. The ACK signal transmitted corresponds to thespecific preamble structure transmitted on the uplink. Once the remotestation detects the ACK signal corresponding to transmitted preamble bythe remote station, the remote station begins transmission of its data.

Corresponding with the preamble structure in the uplink there is acorresponding in time power control information symbol and acorresponding in time collision detection field. Upon start of datatransmission the remote station uses the downlink transmitted powercontrol information to adjust its transmitted power. The power controlsymbols are decoded to derive a binary decision data, which is then usedto increase or decrease the transmitted power accordingly. FIG. 11 showsthe structure of the uplink frame and the slot format for the dataportion of the uplink transmission. Data and control information istransmitted in an in-phase and quadrature-phase multiplexed format. Thatis, the data portion could be transmitted on the in-phase coordinate andthe control portion on the quadrature-phase coordinate. The modulationfor the data and control is BPSK. The control channel contains theinformation for the receiver to enable the demodulation of the data. Thecontrol channel provides for upper layer system functionality. The dataportion consists of one or more frames. Each frame consists of a numberof slots. As an example the frame duration could be 10 milliseconds longand the slot duration 0.625 milliseconds long. In that case, there are16 slots per frame. The beginning of the data payload contains acollision detection field used to relay information about thepossibility of collision with other simultaneously transmitting remotestations. The collision detection field is read by the base station. Thebase station expects the presence of the collision detection field sinceit had provided an ACK signal at the last time slot.

The collision detection field includes a temporary identification (ID)number chosen at random by the mobile for the transmission of thecurrent packet. The base station reads the collision detection field andreflects, or transmits back, the collision detection field on thedownlink. If the collision detection field detected by the remotestation matched the one just being transmitted by the same remotestation, then the collision detection field is an identification thatthe transmission is being received correctly. The remote station thencontinues transmitting the remaining of the packet. In case thecollision detection field has not been received correctly by the remotestation, then the remote station considers the packet reception by thebase station as erroneous and discontinues transmission of the remainingpacket.

The function of the remaining fields are as follows. The Pilot fieldenables the demodulation of both the data and control bits. Thetransmitted power control (TPC) bits are used to control the power of acorresponding downlink channel, in case a down link channel directed tothe same user is operational. If the downlink channel were notoperational, then the TPC control bits can be used to relay additionalpilot bits instead.

The Rate Information (RI) field is used to provide the transmitter withthe ability to change its data rate without the necessity to explicitlynegotiate the instantaneous data rate with the base station. The servicefield provides information of the particular service the data bits areto be used for. The length field specifies the time duration of thepacket. The signal field can be used to provide additional controlinformation as required.

Additional functionalities of the common packet channel are:

(1) Bandwidth Management and (2) L2 Acknowledgment Mechanism.

The bandwidth management functionality is implemented via signalinginformation on the down link common control channel. There are threeways for incorporating this functionality. The first relies on changingthe priority status of all uplink users, which currently aretransmitting information using the CPCH. By this method all the usersare remapping their priority status via a control signal sent at thedownlink. When the priority of the CPCH users is lowered their abilityto capture an uplink channel is lowered. Thus the amount of data sent onthe uplink by the CPCH users is thus reduced. The other mechanism is forthe base station to relay the maximum possible data rate the CPCH usersare allowed to transmit. This prevents the CPCH users from transmittingat a rate which could possibly exceed the uplink system capacity andtherefore take the cell down, i.e., disrupt the communication for allusers currently connected to the base station. For the third method, thebase station could provide a negative acknowledgment through the ACKsignal. In this case, any remote station which is tuned to receive theACK signal is prohibited from further transmission of an access-burstsignal.

The L2 acknowledgment (L2 ACK) mechanism, which is different than the L1ACK, is used by the base station to notify the remote station for thecorrectness of an uplink packet reception. The base station could eitherrelay to the remote station which portions of the packet have beenreceived correctly or which have been received incorrectly. There aremany existing ways of implementing a particular protocol to relay thistype of information. For example, the packet could be identified asconsisting of a number of frames, with each frame consisting of a numberof sub-frames. The frames are identified by a predetermined number. Thesub-frames in each frame are also identified by a specific number. Oneway for the base to relay the information about the correctness of thepacket is to identify all the frames and sub-frames that have beenreceived correctly. Another way is to identify the frames and sub-framesthat have been received in error. The way the base station couldidentify the correctness of a frame or sub-frame is by checking itscyclic residue code (CRC) field. Other more robust mechanisms foracknowledgment may be used. For example, a negative acknowledgment maybe part of the common packet channel. The base station could send anegative acknowledgment (ACK), as part of the L1 ACK, in order to forcethe remote station from transmitting the message part.

CD Operation

There are many remote stations that might try to access the base stationat the same time. There is a number of different preamble signals whicha remote station can use for reaching the base station. Each remotestation chooses at random one of the preamble signals to use foraccessing the base station. The base station transmits a broadcastcommon synchronization channel. This broadcast common synchronizationchannel includes a frame timing signal. The remote stations extract theframe timing transmitted by the base station by receiving the broadcastcommon synchronization channel. The frame timing is used by the remotestations to derive a timing schedule by dividing the frame duration in anumber of access slots. The remote stations are allowed to transmittheir preambles only at the beginning of each access slot. The actualtransmit times for different remote stations could be slightly differentdue to their different propagation delays. This defines an accessprotocol commonly known as the slotted ALOHA access protocol. Eachremote station repeatedly transmits its preamble signal until the basestation detects the preamble, acknowledges that the preamble isreceived, and the acknowledgment is correctly received by the remotestation. There could be more than one remote station transmitting thesame preamble signal in the same access slot. The base station cannotrecognize if two or more remote stations were transmitting the samepreamble in the same access slot. When the base station detects thetransmission of a preamble signal, it transmits back an acknowledgmentmessage. There is one acknowledgment message corresponding to eachpossible preamble signal. Therefore, the are as many acknowledgmentmessages as there are preamble signals. Every transmitting remotestation which receives an acknowledgment message corresponding to itstransmitting preamble signal, will start transmitting its message. Foreach preamble signal, there is a corresponding spreading code used bythe base station to transmit the message. The message transmissionalways starts at the beginning of an access slot. Since there could be anumber of remote stations using the same preamble signal in the sameaccess slot, they start transmitting their message at the same timeusing the same spreading code. In that case, the transmissions of theremote stations likely interferes with each other and thus is notreceived correctly.

Each remote station includes a collision detection (CD) field in thebeginning of the transmitted message. The CD field is chosen at randomby each remote station and independently from each other Remote Station.There is a predefined limited number of CD fields. Two remote stationstransmitting their message at the same time most likely chose adifferent CD field. When the base station receives the CD field, thebase station reflects back, transmits back, the CD field to the remotestation. The remote station reads the reflected CD field by the basestation. If the reflected CD field matched the CD field the remotestation transmitted, the remote station assumes that the remote stationis being received correctly by the base station and continuestransmitting the rest of the message, or data. If the reflected CD fieldfrom the base station did not match the one transmitted by the remotestation, then the remote station assumes that there has been a collisionand stops transmitting the remaining message or data.

It will be apparent to those skilled in the art that variousmodifications can be made to the common packet channel of the instantinvention without departing from the scope or spirit of the invention,and it is intended that the present invention cover modifications andvariations of the common packet channel provided they come within thescope of the appended claims and their equivalents.

1. A method of wireless transmission of information, comprising: (a)transmitting a signal comprising a single preamble randomly selectedfrom among a group of available preambles, at a power level; (b)determining if number of preamble transmissions has reached a limit; (c)determining if an acknowledgement corresponding a preamble transmissionis received from a base station; (d) if the number of preambletransmissions has not reached the limit and there has been no receipt ofa corresponding acknowledgement, repeating step (a) at a higher powerlevel and repeating steps (b) and (c); (e) ceasing transmitting of thesignal, upon any determination at (b) that the number of preambletransmissions has reached the limit; and (f) upon any determination at(c) that a corresponding acknowledgement is received from the basestation, initiating transmission of information over a wirelessspread-spectrum uplink channel to the base station.
 2. The method ofclaim 1, further comprising receiving information over a wirelessspread-spectrum downlink channel from the base station.
 3. The method ofclaim 2, wherein the information received from the base stationcomprises any of packet data and power control information.
 4. Themethod of claim 1, wherein the initiating of transmission of informationcomprises: randomly selecting a collision detection symbol from a numberof possible collision detection symbols; transmitting the collisiondetection symbol at a power level the same as the power level used forthe preamble transmission immediately preceding the receipt of thecorresponding acknowledgement; and if a collision detectionacknowledgment corresponding to the collision detection symbol isreceived, transmitting the information over the spread-spectrum uplinkchannel to the base station.
 5. The method of claim 4, wherein theinformation transmitted to the base station comprises at least one ofpacket data and power control information.
 6. The method of claim 4,further comprising receiving information over a wireless spread-spectrumdownlink channel from the base station.
 7. The method of claim 6,wherein the information received from the base station comprises any ofpacket data and power control information.
 8. The method of claim 7,wherein during each repetition of transmitting at (a), power level oftransmission of the pilot signal increases.
 9. The method of claim 1,wherein during each transmitting at (a) the signal further comprises apilot signal.
 10. The method of claim 1, further comprising: receiving aframe timing signal from the base station; wherein each transmitting at(a) involves transmitting the signal comprising the single preamble in atime slot randomly selected from among a plurality of possible timeslots defined in relation to the received frame timing signal.
 11. Amethod of wireless transmission of information, comprising: (a)transmitting a signal comprising a single preamble randomly selectedfrom among a group of available preambles, at a power level; (b)determining if number of preamble transmissions has reached a limit; (c)determining if an acknowledgement corresponding a preamble transmissionis received from the base station; (d) if the number of preambletransmissions has not reached the limit and there has been no receipt ofa corresponding acknowledgement, repeating step (a) at a higher powerlevel, transmitting a pilot symbol, and repeating steps (b) and (c); (e)ceasing transmitting of the signal, upon any determination at (b) thatthe number of preamble transmissions has reached the limit; (f) upon anydetermination at (c) that a corresponding acknowledgement is receivedfrom the base station, randomly selecting a collision detection symbolfrom among a number of possible collision detection symbols; (h)transmitting the collision detection symbol at a power level the same asthe power level used for the preamble transmission immediately precedingthe receipt of the corresponding acknowledgement; (g) if a collisiondetection acknowledgment corresponding to the collision detection symbolis received, transmitting information over a wireless spread-spectrumuplink channel to the base station; and (h) receiving information over awireless spread-spectrum downlink channel from the base station.
 12. Themethod of claim 11, wherein: the information transmitted over thewireless spread-spectrum uplink channel to the base station comprises atleast one of packet data and power control information; and theinformation received over the wireless spread-spectrum downlink channelfrom the base station comprises at least one of packet data and powercontrol information.
 13. The method of claim 11, further comprising:receiving a frame timing signal from the base station; wherein eachtransmitting at (a) comprises transmitting the signal comprising thesingle selected preamble in a time slot randomly selected from among aplurality of possible time slots defined in relation to the receivedframe timing signal.
 14. A spread-spectrum wireless mobile station,comprising: a spread-spectrum transmitter; a spread-spectrum receiver;and a controller coupled to the spread-spectrum receiver for respondingto received signals and coupled for controlling the spread-spectrumtransmitter, such that in operation the wireless mobile station performssteps comprising: (a) transmitting a signal comprising a single preamblerandomly selected from among a group of available preambles, at a powerlevel; (b) determining if number of preamble transmissions has reached alimit; (c) determining if an acknowledgement corresponding a preambletransmission is received from a base station; (d) if the number ofpreamble transmissions has not reached the limit and there has been noreceipt of a corresponding acknowledgement, repeating step (a) at ahigher power level and repeating steps (b) and (c); (e) ceasingtransmitting of the signal, upon any determination at (b) that thenumber of preamble transmissions has reached the limit; and (f) upon anydetermination at (c) that a corresponding acknowledgement is receivedfrom the base station, initiating transmission of information over awireless spread-spectrum uplink channel to the base station.
 15. Themobile station of claim 14, wherein the initiating of transmission ofinformation comprises: randomly selecting a collision detection symbolfrom a number of possible collision detection symbols; transmitting thecollision detection symbol at a power level the same as the power levelused for the preamble transmission immediately preceding the receipt ofthe corresponding acknowledgement; and if a collision detectionacknowledgment corresponding to the collision detection symbol isreceived, transmitting the information over the spread-spectrum uplinkchannel to the base station.
 16. The mobile station of claim 14, whereinat least during a repetition of (a), the signal transmitted furthercomprises a pilot signal following the selected preamble.
 17. The mobilestation of claim 14, wherein: the controller is for controllingoperation of the remote station for performing the additional stepcomprising receiving a frame timing signal from the base station; andeach transmitting of the signal at (a) involves transmitting the signalcomprising the single preamble in a time slot randomly selected fromamong a plurality of possible time slots defined in relation to thereceived frame timing signal.
 18. A base band processor for use in aspread-spectrum wireless remote station, comprising: an acknowledgmentdetector for detecting an acknowledgment in received spread-spectrumsignals; a data and control processor, for detecting and processing dataand control information contained in received spread-spectrum signals; aencoder, for encoding data; a preamble generator for generatingpreambles; a multiplexer for multiplexing the encoded data and thepreambles; a packet formatter, coupled to the multiplexer, forformatting the multiplexed data and preambles into packets; and acontroller coupled to the acknowledgment detector for controlling thepreamble generator, the multiplexer and the packet formatter, such thatin operation the base band processor performs steps comprising: (a)transmitting a signal comprising a single preamble randomly selectedfrom among a group of available preambles, at a power level; (b)determining if number of preamble transmissions has reached a limit; (c)determining if an acknowledgement corresponding a preamble transmissionis received from a base station; (d) if the number of preambletransmissions has not reached the limit and there has been no receipt ofa corresponding acknowledgement, repeating step (a) at a higher powerlevel and repeating steps (b) and (c); (e) ceasing transmitting of thesignal, upon any determination at (b) that the number of preambletransmissions has reached the limit; and (f) upon any determination at(c) that a corresponding acknowledgement is received from the basestation, initiating transmission of information over a wirelessspread-spectrum uplink channel to the base station.
 19. The base bandprocessor of claim 18, wherein the initiating of transmission ofinformation comprises: randomly selecting a collision detection symbolfrom a number of possible collision detection symbols; transmitting thecollision detection symbol at a power level the same as the power levelused for the preamble transmission immediately preceding the receipt ofthe corresponding acknowledgement; and if a collision detectionacknowledgment corresponding to the collision detection symbol isreceived, transmitting the information over the spread-spectrum uplinkchannel to the base station.
 20. The base band processor of claim 18,wherein at least during a repetition of (a), the signal transmittedfurther comprises a pilot signal following the selected preamble. 21.The base band processor of claim 18, wherein: the controller is forcontrolling operation of the base band processor for performing theadditional step comprising receiving a frame timing signal from the basestation; and each transmitting of the signal at (a) involvestransmitting the signal comprising the single preamble in a time slotrandomly selected from among a plurality of possible time slots definedin relation to the received frame timing signal.
 22. The base bandprocessor of claim 18, further comprising: a spread-spectrum modulatorfor modulating formatted packets from the packet formatter fortransmission over the wireless uplink channel; and a spread-spectrumdemodulator for demodulating the received spread-spectrum signals. 23.The base band processor of claim 22, further comprising an interleaverfor interleaving encoded data from the encoder and supplying interleavedencoded data to the packet formatter.